Billbergia’s 39-story tower, Rhodes Central, is home to the largest Heliostat in Sydney. The structure is far more than just an architectural feature, more so a piece of world-leading technology that confirms Australia’s status as a leader in solar innovation.

Deriving its name from the Greek words for sun (helio) and stationary (stat), the heliostat is designed to capture the sun’s light energy using a series of custom-made smart mirrors. The mirrors and reflectors autonomously shift and tilt towards the sun and then reflect the sunlight onto the Union Square Plaza, which was previously covered in shadow.

While most heliostats are used to collect energy for solar electric power plants in remote locations, Billbergia’s Rhodes Central heliostat is one of only two known structures in the world to sit atop a mixed-use development. The other is also located in Sydney, at One Central Park.

Alex Lehmann, Research Scientist at Heliosystems and the designer of the heliostat at Rhodes Central, says metropolitan buildings are not the typical home of a heliostat, but bring with them a multitude of benefits.

“It’s only very recently that heliostats have been adapted for this kind of architectural use, and we are only just beginning to understand what you can do with active and passive lighting in our cities,” he says.

“Buildings are getting taller and we have options as to where we can direct light to improve the amenity of public spaces on the ground. This latest generation technology heliostat showcases an exciting opportunity for developers to think about lighting in public spaces and to be more creative with how they use sunlight to change the urban environment.”

The Rhodes Central heliostat comprises several complex parts. One key element is the large golden crown-like structure clearly visible on top of the building. Built to exacting standards, it uses high-quality structural steel that has been finished and wrapped in gold-coloured, solid aluminium panels.

A network of sun-tracking motorised mirrors follow the sun’s movement during the day, which are concealed from onlookers. Sunlight is bounced from the mirrors on the roof up to the second set of reflector mirrors in the golden crown, that then direct the sunlight back down towards Union Square Plaza. Plastic sheeting covers the reflective surface and filters out UV light in order to ensure harmful UV rays are not directed towards the plaza.

The heliostat is the result of a collaborative partnership between HeliostatSA, SJB Architecture, Inhabit Technical Design and Samaras Engineering.

“For us, the challenges were in solving the engineering details, such as how to make the optics work. To maximise the energy reflected down to the park, we worked hard to integrate a large heliostat collection area on the roof. However, the reflectors on the crown present a relatively smaller area, so we had to focus the sunlight slightly at the reflectors before it diverges again on the way down to the park,” says Lehmann.

The team also installed a weather station on the roof that monitors conditions. The heliostat responds to the conditions, with the autonomous reflectors putting themselves in a brace position if it’s windy, and in a position to be washed when it rains. If in the event of a hailstorm, the reflectors tilt themselves into a position to minimise damage.

Lehmann explains that unlike heliostats that are surrounded by desert, the Rhodes Central structure had to meld with other elements of the building.

“This heliostat has had to be integrated with other facilities in the building and it has to work well with other functions on the roof. All in all, coming up with the right design has been quite an intense process and a lot has been learned along the way.”

When the sun goes down, the heliostat showcases its ‘night glow’ feature that outlines its structural design.

“At night, the reflectors glow an interesting colour and people will see some interesting lighting displays happening,” said Mr Lehmann.

“The heliostat is a feature of the Rhodes skyline now and as it becomes part of people’s living space; I hope they enjoy what it offers to the Rhodes community.”